No abstract

The crystal structure of the ordered form of solid methylchloroform (1,1,1-trichloroethane) has been determined from three-dimensional x-ray film data, collected at −60° and −145°. The data revealed no significant structural differences between the solids at these temperatures. The existence of a crystal-lographic phase transition at −68° is thus ruled out. The crystals are orthorhombic, space group, Pnma, with four molecules per unit cell. The lattice dimensions are a=11.53(1) Å, b=8.000(5) Å, c=5.88(1) Å at −60° and a=11.46(1) Å, b=7.890(5) Å, c=5.81(1) Å at −145°. The C–Cl distance is 1.782(16) Å. Analysis of the thermal parameters indicate that at −60° there is a greater degree of librational motion about the C–C axis than at −145°.

No abstract

A general purpose automatic low temperature system, which generates a stable stream of cold gas, can be used for maintaining frost-free samples at any temperature between ambient and 100 K. In this system cold nitrogen gas, obtained from boiling liquid nitrogen, is warmed to room temperature, controlled by standard noncryogenic components, and recooled by passing it through a heat exchanger immersed in the liquid nitrogen. The system also incorporates a novel level controller consisting of a magnet riding on the level indicator float which activates magnetic reed switches attached to the exterior of this indicator. The application of this apparatus in the field of x-ray diffraction is described.